As a bowler, I think Imran Tahir would have been a better choice than Moin Ali. But if you say that Imran Tahir is not very good at batting, it is true. I think Moin Ali will be included in the squad as an all-rounder. It's not that England is just bowling badly. They are batted very badly too. At the moment there is no option to take spinner all-round in the squad now. I think Moin Ali is a good choice. Ngidi can be kept in the team to increase the strength in the pace bowling lineup.
If Moeen Ali is included in the playing XI, then there is no point in including Imran Tahir. They don't need to waste two overseas slots on spinners. Also, they have good Indian spinners in the form of Ravindra Jadeja and Karn Sharma. And in case they are so adamant about including an overseas spinner, then IMO Mitchell Santner may be a much better choice. I would like the CSK to go with at least one overseas pacer, probably Josh Hazlewood.